The mechanisms involved in the development of radiation nephritis are poorly understood, particularly with respect to man. Studies employing whole body exposure of rodents and those in the dog utilizing in-situ renal irradiation have failed to correlate altered function with abnormal structure. We have chosen a nonhuman primate as the experimental animal because renal function and structure of a number of nonhuman primates are known to be similar to man. The studies in progress are designed to 1) evaluate radiation nephritis in the monkey; 2) correlate altered renal function with abnormal structure as a function of x-ray dose and time after exposure; 3) administed radiation within the therapeutic range to one kidney and 4) divide the urinary bladder by the method of Bricker to allow split function studies for comparison of the function of the irradiated kidney with the nonexposed kidney.